In the manufacture of cigarettes, cut tobacco is metered from a reservoir or hopper of tobacco to provide a metered flow, a vertically-moving thin shower of tobacco particles is formed from the metered flow, a tobaco filler rod is formed from the shower of tobacco particles, and a paper web is wrapped around the tobacco filler rod.
Since there is a tendency for the tobacco filler rod to have variable quantities of tobacco at various locations along its length, giving rise to a variable thickness, there is usually first formed from the shower of tobacco particles a rod of tobacco particles containing a greater quantity in the cross-section thereof over that ultimately required in the tobacco filler rod, and excess tobacco is trimmed from the rod of tobacco particles to provide the tobacco filler rod for wrapping and trimmed tobacco. This procedure of overfeeding and then trimming ensures that all locations along the length of the rod have the thickness of tobacco required to form the cigarette.
Trimmed tobacco usually is recycled to the hopper of tobacco from which the metered flow is formed. The metered flow of tobacco from which the tobacco shower is formed generally is provided from a tobacco hopper with some form of refuser mechanism, such as carding drums, to control and meter the quantity of tobacco which passes to the rod-forming operation from the hopper. Such refuser mechanisms, which may also involve recycle of tobacco to the hopper, result in degradation of tobacco, thereby impairing the filling power of the tobacco.
In most cigarette-making machines, the feeder speed, i.e. the refuser roll metering, is not normally continuously controlled but rather is preset to a desired average flow rate and, as a result of variations in density, the mosture content of the tobacco, particle size and similar variations, variable flow rates of tobacco occur, leading to variations in quantities of tobacco trimmed. Any tobacco which is trimmed becomes degraded, thereby impairing its filling power, and hence it is desirable to control the amount of trimming to take into account the variations noted above.
Prior attempts have been made to use trimmed tobacco as a rod-formation control. In U.S. Pat. No. 3,431,914, there is described a procedure in which trimmed tobacco is fed to a storage vessel, tobacco from the storage vessel is returned to the rod of tobacco particles formed from the shower, and the amount of tobacco withdrawn from the storage vessel and recycled is regulated in accordance with testing the quantity of tobacco in the filler rod after trimming or the rod of tobacco particles before trimming. In addition, the amount of trimmed tobacco in the storage vessel is sensed, with the amount of rising and falling dependent on the amount of excess tobacco trimmed. If the amount of tobacco in the storage vessel is sensed to be too great, then the mechanism for forming the vertically-moving tobacco shower is regulated to decrease the tobacco feed rate. The rate of removal of the tobacco from the trimmed tobacco storage vessel, however, is controlled by measurements conducted on the rod prior to or after trimming. Two independent measurements are made and two different operational controls result from these measurements.
U.S. Pat. No. 4,095,604 describes a tobacco metering device which comprises a generally vertically-extending thin and laterally-wide channel in which tobacco particles fed from a hopper by a carding drum and picker combination pile up to form a carpet between the front and rear wall of the channel. One of the walls of the channels is movable to permit the carpet of tobacco to be fed downwards through the channel and a conveyor is provided at the lower end of the channel for forwarding the carpet towards the formation of the vertically-moving shower.
In one embodiment of this prior art device, trimmed tobacco is fed into the upper end of the channel across one part of the width of the channel while new tobacco from the hopper is fed across the remainder of the width of the channel, so that the carpet of tobacco in the channel is formed of side-by-side portions of new tobacco and recycled trimmed tobacco. Provided at the lower end of the channel are a pair of independently-operated carding rollers, so as to feed tobacco independently from the side-by-side portions of the carpet. The height of tobacco in the side-by-side portions of the carpet is independently sensed and such sensings are used to control independently the speed of the carding rollers to maintain the levels of the side-by-side portions within predetermined levels.
In this prior art device, therefore, recycled trimmed and new tobacco are provided side-by-side in a carpet confined between vertical front and rear walls, the height of the respective portions is sensed and the flow rate of tobacco from the respective portions is independently controlled as a result of independent measurements.
As far as the applicant is aware, there has been no published attempt to use the feed rate of recycled trimmed tobacco as the control mechanism for the metering of cut tobacco from a reservoir thereof to form a metered flow.